Pressurized fluid containers are in widespread use for packaging and dispensing a variety of fluid products, including liquids, gases, solids and combinations thereof. Under normal operating conditions such containers perform entirely satisfactorily. However, in the event that the contents of such containers become over-pressurized, either because of improper use, exposure to heat or for any other reason, then a violent rupture may occur. The art has provided a variety of pressure relief devices for aerosol cans to prevent explosion of the pressurized can by controlled pressure release prior to catastrophic failure. Many of these pressure relief devices are in the bottom of the can, while some are in the body sidewall or top.
By way of example only, one category of pressure relief devices provides one or more concave regions in the bottom of the can in combination with coined lines of reduced material thickness. In this regard, it is to be understood that the term “coin” or “coining” denotes a process of removing or displacing metal to achieve a desired indentation profile with an underling web at the base of the indentation. Coining includes scoring and/or applied pressure techniques as will be well known to those of skill in the art. In operation, the bottom fractures along the coined lines in response to an over pressurization of the container contents thereby creating vent openings. A controlled and predictable release of pressure is thus provided.
One known system for controlled pressure release is provided in U.S. Pat. No. 4,513,874 to Mulawski. Another system which has been found to be highly effective is disclosed in U.S. Pat. No. 7,222,757 to Ferreira et al. Yet another system which is highly effective is disclosed in U.S. published patent application 2013/0020320 to Ferreira et al. The contents of all references identified herein are hereby incorporated by reference as if fully set forth in their entirety.
Typically, in past devices the coined line in the bottom has experienced fracture and corresponding controlled pressure relief at internal pressures of about 380 psig to about 450 psig. However, in some instances venting at the desired pressure may not occur as intended. By way of example only, and not limitation, factors which may prevent fracture and venting at the intended pressure may include the introduction of a coin depth which is too shallow due to tooling variations and/or variations in the starting material thickness of the material forming the can bottom such that the web of material remaining at the base of the coined line after introduction is slightly thicker than intended.
In many prior venting systems using coined bottoms, there has been a reversal of the can bottom in the event that the vent does not activate at the intended pressure. That is, in the event that venting by bottom fracture does not take place at the prescribed pressure level as intended, the pressure eventually may be relieved by a reversal failure at the bottom such that the concave dome of the bottom undergoes eversion wherein the bottom reverses upon itself to develop a bulging convex profile and eventually fails by bursting or separating from the body to permit escape of the pressurized contents.
It is generally desirable for the normal venting pressure to be relatively high to avoid premature venting at pressures experienced due to variations in environmental conditions during storage and/or use. At the same time, it may be desirable for the can bottom to have an eversion pressure resulting in reversal failure which is significantly greater than the intended venting pressure. However, in the past, it has been difficult to achieve ultimate strength levels in a coined container bottom that allow the container bottom to withstand pressures significantly above about 500 psig before reversal failure will take place. Thus, the designed venting pressure has typically been below about 500 psig to account for variability due to material thicknesses and the like. However, the designed venting pressure may not be set too low or unintended premature venting may take place.
Consequently, there is a continuing need for a pressure relief device having a coined pressure vent characterized by a normal venting pressure of greater than 500 psig before venting and a suitable eversion pressure to avoid reversal failure.